Circuit arrangement

Abstract

A ballast arrangement is provided for igniting and operating a discharge lamp. The lamp is connected in a commutating bridge in series with an inductor and parallel to a capacitor. The inductor and the capacitor together form a resonance circuit. During ignition, the bridge is commutated at a comparatively high frequency that changes with respect to time. The series resonance circuit has a resonance frequency that is close to an odd harmonic of the comparatively high frequency.

1. A ballast arrangement for a discharge lamp with resonant ignition, comprising a coil, wherein said coil is situated in a diagonal branch of a bridge-shaped commutation circuit, and wherein said coil is arranged in series with electrical lamp connections, and a capacitor arranged in parallel with said electrical lamp connections, which commutation circuit supplies a comparatively low-frequency square-wave supply voltage of comparatively small amplitude to the lamp in a normal operating phase of the lamp wherein an arc discharge takes place continuously in the lamp, and, in an ignition phase preceding the normal operating phase, the commutation circuit is commutated at a comparatively high-frequency by a switching voltage at a switching frequency that varies with respect to time, wherein, in the ignition phase, an odd harmonic frequency of the switching frequency is substantially equal to a resonant frequency of said coil and said capacitor, and wherein the switching frequency is decreased to an intermediate value between substantially one third of the resonance frequency and an operating frequency of the discharge lamp during a warm-up phase between the ignition phase and the normal operating phase. 
     
     
       2. The ballast arrangement as claimed in  claim 1 , wherein said odd harmonic frequency is the third harmonic. 
     
     
       3. The ballast arrangement as claimed in  claim 1 , wherein a voltage-detection circuit is coupled to the electrical lamp connections in order to detect a predetermined value of an ignition voltage of the lamp and then supply an indication signal for maintaining the variation of the switching frequency. 
     
     
       4. The ballast arrangement as claimed in  claim 3 , wherein said voltage detection circuit also serves to stabilize the ignition voltage at a value that is at least close to said predetermined value. 
     
     
       5. The ballast arrangement of  claim 1 , wherein the switching frequency is decreased to a further intermediate value between the intermediate value and the operating frequency during the warm-up phase. 
     
     
       6. A ballast arrangement for a discharge lamp comprising:
 an inductor arranged in series with the discharge lamp; and 
 a capacitor arranged in parallel with the discharge lamp, the inductor and the capacitor forming a resonance circuit having a resonance frequency; 
 wherein, in an ignition phase, an odd harmonic frequency of a switching frequency of a voltage supplied to the discharge lamp is substantially equal to the resonance frequency; and 
 wherein the switching frequency is decreased to an intermediate value between substantially one third of the resonance frequency and an operating frequency of the discharge lamp during a warm-up phase between the ignition phase and a normal operating phase of the discharge lamp. 
 
     
     
       7. The ballast arrangement of  claim 6 , wherein the odd harmonic frequency is a third harmonic of the switching frequency. 
     
     
       8. The ballast arrangement of  claim 6 , wherein the switching frequency is decreased to a further intermediate value between the intermediate value and the operating frequency during the warm-up phase. 
     
     
       9. A ballast arrangement for a discharge lamp comprising:
 an inductor arranged in series with the discharge lamp; 
 a capacitor arranged in parallel with the discharge lamp, the inductor and the capacitor forming a resonance circuit having a resonance frequency; and 
 a voltage-detection circuit coupled to the discharge lamp and configured to detect a predetermined value of a voltage supplied to the discharge lamp and then supply an indication signal for maintaining a switching frequency of the voltage supplied to the discharge lamp at substantially one third of the resonance frequency, 
 wherein, in an ignition phase, an odd harmonic frequency of the switching frequency is substantially equal to the resonance frequency; and 
 wherein the switching frequency is decreased to an intermediate value between substantially one third of the resonance frequency and an operating frequency of the discharge lamp during a warm-up phase between the ignition phase and a normal operating phase of the discharge lamp. 
 
     
     
       10. The ballast arrangement of  claim 9 , wherein the odd harmonic frequency is a third harmonic of the switching frequency. 
     
     
       11. The ballast arrangement of  claim 9 , wherein the switching frequency is decreased to a further intermediate value between the intermediate value and the operating frequency during the warm-up phase. 
     
     
       12. A ballast arrangement for a discharge lamp comprising:
 an inductor arranged in series with the discharge lamp; and 
 a capacitor arranged in parallel with the discharge lamp, the inductor and the capacitor forming a resonance circuit having a resonance frequency; 
 wherein, in an ignition phase, an odd harmonic frequency of a switching frequency of a voltage supplied to the discharge lamp is substantially equal to the resonance frequency, and wherein a ratio of the resonance frequency to the switching frequency is substantially 3:1 so that a dimension of the capacitor is decreased; 
 wherein the switching frequency is decreased to an intermediate value between substantially one third of the resonance frequency and an operating frequency of the discharge lamp during a warm-up phase between the ignition phase and a normal operating phase of the discharge lamp. 
 
     
     
       13. The ballast arrangement of  claim 12 , wherein the switching frequency is decreased to a further intermediate value between the intermediate value and the operating frequency during the warm-up phase.